Fungi wars: parasites use 'guerrilla tactics' and chemical weapons to infect animal hosts
Parasitic fungi which enter animals' bodies and feed on their insides use guerrilla warfare-style tactics, penetrating and destroying the immune system with small troops before a large scale attack, a new study has revealed.
In theory, an animal's immune system should be able to detect and fight off parasites before they gain a significant foothold, but some types of fungi are able to bypass even the best defences.
"Evolution has turned [the fungi] into a highly sophisticated and efficient war machine, with everything from ammunition production lines to special operation units," said lead researcher Wang Chengshu, of the Chinese Academy of Sciences' Shanghai Institute for Biological Science.
In a paper in the US journal Proceedings of the National Academy of Science, Wang and his colleagues described for the first time how fungi generated and used small chemical agents to infiltrate prospective hosts' immune systems and open a gate for further infection.
The scientists identified a "chemical weapon production line" consisting of seven genes in Beauveria bassiana, one of the deadliest fungi to insects. The genetic "factory" produces a chemical called bibenzoquinone oosporein, used against potential hosts to weaken them before infection.
"The production of the chemical is an extremely sophisticated but organised process, with every gene playing a specific function like workers in a production line," Wang said.
"Because the fungus cannot create high temperatures or pressure like in a human factory, the genes must break the production into many tiny, delicate steps. It's a wonder of nature that has been eluding us for a long time."
In the past, it was thought that fungi attacked animals with large molecules such as proteins. These proteins acted as planes and tanks in the war against the host's immune system, but could be fought off.
The discovery of the chemical "guerrilla" agents would help us better understand how the fungus attacked, Wang said.
Though the fungus examined in the study was only deadly to insects, some fungi which target animals or humans may also use similar strategies to penetrate their hosts' immune systems.
The study took the researchers three years to complete, but Wang said they felt lucky. The fungus had more than 10,000 genes, around half of a human, and to identify the ones involved in the production of the "guerrilla" chemicals was incredibly difficult.
Some questions remain unanswered however.
For instance, the researchers were unclear on how the chemicals sabotaged the host's entire immune system, and whether the same strategy was used by fungi species deadly to humans as well.